Unit Testing App Engine with Gorilla MUX

Question

I want to write tests for handlers in Google App Engine that use Gorilla mux to read variables from the request URL.

I understand from the documentation that you can create a fake context and request to use with testing.

I'm calling the handler directly in the test but the handler isn't seeing the path parameter as expected.

func TestRouter(t *testing.T) {
  inst, _ := aetest.NewInstance(nil) //ignoring error for brevity
  defer inst.Close()
  //tried adding this line because the test would not work with or without it
  httptest.NewServer(makeRouter())
  req, _ := inst.NewRequest("GET", "/user/john@example.com/id-123", nil)
  req.Header.Add("X-Requested-With", "XMLHttpRequest")
  resp := httptest.NewRecorder()
  restHandler(resp, req)
}

func restHandler(w http.ResponseWriter, r *http.Request) {
  ctx := appengine.NewContext(r)
  params := mux.Vars(r)
  email := params["email"]
  //`email` is always empty
}

The problem is that the handler always sees an empty "email" parameter because the path is not interpreted by Gorilla mux.

The router is as below:

func makeRouter() *mux.Router {
  r := mux.Router()
  rest := mux.NewRouter().Headers("Authorization", "").
    PathPrefix("/api").Subrouter()

  app := r.Headers("X-Requested-With", "XMLHttpRequest").Subrouter()
  app.HandleFunc("/user/{email}/{id}", restHandler).Methods(http.MethodGet)

  //using negroni for path prefix /api
  r.PathPrefx("/api").Handler(negroni.New(
    negroni.HandlerFunc(authCheck), //for access control
    negroni.Wrap(rest),
  ))
  return r
}

All my searches have not gotten anything specific to App Engine unit testing with Gorilla mux.

Answer 1

Since what you're testing is the handler, you could just get an instance of the router and call ServeHTTP on it. Here is how it should be based on your code.

main.go

func init() {
    r := makeRouter()
    http.Handle("/", r)
}

func makeRouter() *mux.Router {
    r := mux.NewRouter()
    app := r.Headers("X-Requested-With", "XMLHttpRequest").Subrouter()
    app.HandleFunc("/user/{email}/{id}", restHandler).Methods(http.MethodGet)

    return r
}

func restHandler(w http.ResponseWriter, r *http.Request) {
    params := mux.Vars(r)
    email := params["email"]
    fmt.Fprintf(w, email)
}

main_test.go

func TestRouter(t *testing.T) {
    inst, _ := aetest.NewInstance(nil) //ignoring error for brevity
    defer inst.Close()

    req, _ := inst.NewRequest("GET", "/user/john@example.com/id-123", nil)
    req.Header.Add("X-Requested-With", "XMLHttpRequest")
    rec := httptest.NewRecorder()

    r := makeRouter()
    r.ServeHTTP(rec, req)

    if email := rec.Body.String(); email != "john@example.com" {
        t.Errorf("router failed, expected: %s, got: %s", "john@example.com", email)
    }
}

Notice I removed the rest routes since that's not part of your test, but the idea would be the same. Also didn't check for errors for simplicity.